I'm not familiar with the error code you provided. Is this still a problem for you now that the weekend has passed? I ask because I'm not sure if this was some kind of transient error.
"Sync over cellular" is only a relevant option if your device has cellular functionality. Is it safe to say your device has stable WiFi? Have you recently changed any network settings, started using a VPN, etc?
If this problem still occurs, does it help to force-quit and relaunch the app?
Or re-install the app? NOTE: if you have local changes that have sync pending when you tap on the cloud icon, please do not delete the app or those unsynced changes will be lost. In this case, I'd advise you to do a full iTunes/iCloud device backup so that Lightroom and any unsynced files can be restored... and only after backing up should you try to reinstall the app.